Three cases having typical mongoloid features and few or no features of Turner's syndrome were reported. Four distinct stem lines of cells 45,X/46,X,+G/46,XX and 47,XX,+G were found to be present in the lymphocytes of two females. In the third case, only three stem lines were found, the 45,X line being absent. The proportion of cell lines was different in each case. Possible mechanisms for the mosaicism were suggested.